1. Field of the Invention
The present invention relates to a method of manufacturing a photovoltaic device for directly converting light energy such as solar rays to electric energy.
2. Description of the Prior Art
While exhaustion of energy resources has become a problem, photovoltaic devices such as solar cells for directly converting light energy to electric energy have been developed, inasmuch as they utilize the inexhaustible solar rays as a major energy source.
FIG. 1 is a perspective view showing a portion of a photovoltaic device manufactured in accordance with a conventional method. Referring to FIG. 1, the device shown comprises an insulating substrate 1 of glass, transparent plastic or the like, and a plurality of photoelectric converting regions 2a, 2b, 2c formed side-by-side on a main surface of the insulating substrate 1. The converting regions 2a, 2b, 2c comprise first electrode layers 3a, 3b, 3c of a transparent conductive oxide material such as tin oxide (SnO.sub.2), indium tin oxide (In.sub.2 O.sub.3 --SnO.sub.2), or the like formed on the insulating substrate 1, film-like photoelectric semiconductor layers 4a, 4b, 4c of amorphous silicon or the like having a PIN junction structure, the regions of which are arranged in the order of PIN from the light receiving side, and formed on the first electrodes 3a, 3b, 3c, respectively, and second electrode layers 5a, 5b, 5c of aluminum or the like in ohmic contact with the photoelectric semiconductor layers 4a, 4b, 4c, respectively, thereby to form a layered structure including the above described layers.
FIG. 2 is an enlarged sectional view of a major portion of the device shown in FIG. 1. As better seen in FIG. 2, the photoelectric converting regions 2a, 2b, 2c provided side by side as described above are adapted such that extensions 5a', 5b' of the second electrode layers 5a, 5b extending from the upper surfaces of the photoelectric semiconductor layers 4a and 4b are directly coupled to exposed portions 3b', 3c' of the first electrode layers 3b, 3c exposed on the insulating substrate 1 from the lower surface of the right adjacent photoelectric semiconductor layers 4b, 4c, respectively, whereby the plurality of photoelectric converting regions 2a, 2b, 2c are electrically connected in series.
One of the factors influencing the light utilization efficiency in such device is the ratio of the total area of the photoelectric converting regions 2a, 2b, 2c actually contributing to photoelectric conversion with respect to the light receiving area of the whole device, i.e. the area of the substrate. However, the isolating regions inevitably existing in the spaces between the respective adjacent photoelectric converting regions 2a, 2b, 2c reduce the above described ratio of the areas.
Accordingly, in order to improve the light utilization efficiency, it is necessary to reduce the isolating regions of the spaces between the respective adjacent photoelectric converting regions 2a, 2b, 2c. Reduction of such spaces, however, is determined by the precision in formation of the respective layers and accordingly a photoetching technology of very high resolution is desired. In the case of such technology, the steps of depositing the first large area electrode layer on the whole surface of the substrate 1, and dividing the same into the individual first electrode layers 3a, 3b, 3c by means of a photoresist and etching or removing the spaces between the respective adjacent first electrode layers 3a, 3b, 3c, are carried out in succession and then the similar steps of depositing and removing are again repeated for the photoelectric semiconductor layer 4a, 4b, 4c and the second electrode layers 5a, 5b, 5c.
However, since the above described photoetching technology involves a wet process such as rinsing, it could happen that pin holes are formed in the film-like photoelectric semiconductor layers 4a, 4b, 4c, in which case the material of the second electrodes to be deposited in the subsequent step contacts the first electrode layers 3a, 3b, 3c through such pin holes. As a result, defects occur in which the first electrode layers 3a, 3b, 3c are electrically short-circuited to the second electrode layers 5a, 5b, 5c facing the first electrode layers 3a, 3b, 3c with the photoelectric semiconductor layers 4a, 4b, 4c of the corresponding photoelectric converting regions 2a, 2b, 2c sandwiched therebetween. Furthermore, there is concern that the contacting surfaces of the photoelectric semiconductor layers 4a, 4b, 4c with which the second electrode layers 5a, 5b, 5c are in ohmic contact are degraded by formation and removal of a photoresist and by rinsing in the above described photoetching technology, even if the same are not damaged to the extent that pin holes are formed. Furthermore even a slight amount of moisture left after rinsing could cause corrosion of the second electrode layers 5a, 5b, 5c to be deposited in the subsequent step.